Commercial allergenic extracts are complex mixtures of molecules of which only a few have allergenic activities. Current standardization of allergenic extracts with RAST or ELISA inhibition is based on serum from allergic patients. These assays are not possible to define what is being measured apart from the potency of the extract relative to a reference standard. Sandwich ELISA utilizes two monoclonal antibodies that recognize different epitopes on a specific allergen. This method is specific, sensitive, fast, and reproducible. It measures the quantity of an allergen in the mixture. Using purified Fel D I and commercial monoclonal antibodies, we have quantitated cat pelt extract by sandwich ELISA. We are currently conducting stability study on one commercial lot of cat pelt/hair extract. With the help of Dr. Karpas, we are also in the process of making monoclonal antibodies, this will eliminate the dependency on the limited source of commercial material, and make it possible to implement the assay to commercial companies. ELISA quantitation of DER fI and DER f II are underway.